I have a web site built on Symfony2 which uses twig templates, LESS, and assetic.

In order to cache bust assets, I'm simply using this in my config.yml:

framework:
    templating:
        engines: ['twig']
        assets_version: 'asset-version-here'

And then I use the asset() function to load the asset and the cache busting is handled for me.

However, the concern I have is when I load my LESS (css) file, there are references to other files, and I would like to know how these files can be cache busted as well.

Example:

.someSelector { background:url('../images/filename.png'); }

How can I make sure that the referenced file, filename.png is cache busted upon deployment?

The asset files referenced in Twig using asset() are cache busted automatically upon deployment (I use a deployment script hook that updates the assets_version in the framework's config), but those referenced in a stylesheet are not.

How can I do this?